In accordance with the International Convention for the Prevention of Pollution from Ships (MARPOL Convention), engines operating in the emission control areas (ECAs) must use emission controls that achieve an about 80% reduction in NOx emissions, with respect to ships newly built on or after 2016.
Conventionally, in SCR (selective catalytic reduction) denitration equipment installed in an exhaust passage of an internal combustion engine, for example, diesel engines, etc., or the like, a denitration reaction is not sufficient in a low-temperature exhaust gas atmosphere where an exhaust gas temperature of a vessel is 300° C. or lower, and a denitration catalyst is poisoned by ammonium hydrogen sulfate (acidic ammonium sulfate) resulting from a reaction between a sulfur content contained in fuel oil and an ammonia component of a reducing agent. Thus, there was involved such a problem that it is difficult to achieve practical implementation.
Meanwhile, there are known denitration catalysts using an alcohol as a reducing agent and utilizing a zeolite capable of undergoing denitration in a low temperature region of about 180 to 300° C. In those low-temperature active denitration catalysts, there is confirmed such a problem that the performance is lowered with a lapse of time during the denitration reaction due to deposition (caulking) of a carbon component derived from the alcohol used as the reducing agent onto the denitration catalyst.
In addition, it is confirmed that by extracting such a denitration catalyst whose performance has been lowered and heat treating it, the deposited carbon component detaches, whereby the performance is recovered.
For example, PTL 1 as described below discloses a method of reducing and removing NOx in an exhaust gas by using an alcohol and/or an ether, such as methanol and/or dimethyl ether, etc., as a reducing agent and a denitration catalyst of a proton-type β zeolite; and discloses a denitration catalyst regeneration system in which on that occasion, a denitration catalyst layer is disposed in each of exhaust gas treatment passages of branched at least two systems, one of the exhaust gas treatment passages is closed to stop the supply of the exhaust gas, and while continuing an exhaust gas treatment in the other exhaust gas treatment passage, the denitration catalyst layer of the exhaust gas treatment passage where the supply of the exhaust gas is stopped is heat treated (directly heated by a heater) at 350 to 800° C. on site, thereby recovering the lowered denitration performance.
In addition, in FIG. 2 of PTL 2 as described below, there are disclosed a denitration catalyst regeneration system as function recovery structure of a denitration catalyst of an exhaust treatment apparatus of automobile, in which a first reducing agent-charging pipe for charging a reducing agent at all times and a second reducing agent-charging pipe for charging a reducing agent in due time are installed, and furthermore, in which an oxidation catalyst is inserted with respect to regulation of a reducing agent supply pressure in association with an increase of a back pressure on the upstream side of the denitration catalyst. In the denitration catalyst regeneration system described in this PTL 2, it is described that the exhaust passing through the oxidation catalyst is activated even at the normal time, whereby the reactivity in the sequent denitration catalyst is increased, and furthermore, at the time when the function of the denitration catalyst is lowered due to deposition of a combustion residue, the activity of the oxidation catalyst is more increased by charging the reducing agent from the second system, thereby promoting perfect combustion of the combustion residue.